Conventional rotary extrusion blow molding apparatuses typically have a structural frame mounted on a rotating shaft. The structural frame has a plurality of molds mounted thereon and is known in the industry as a wheel. As the wheel is rotated, the plurality of molds is rotated past an extrusion die extruding a continuous parison. Each mold typically includes two mold halves, each comprising a mold cavity half therein, such that when the mold halves are closed, the mold defines a mold cavity corresponding to the configuration of the article to be molded, such as a container. Each mold, seriatim, is rotated past the extrusion die with the mold halves in an open configuration. The mold halves of each mold are then closed around the parison to enclose the parison within the mold defined by the mold halves. A blowing needle is then inserted into the parison within the closed mold and internal pressure is introduced to the parison, forcing it to inflate and conform to the configuration of the mold cavity. The molded object is then cooled and the mold opened to release the molded object from the mold.
When the two mold halves are clamped over one or more parisons prior to blowing of the parisons to form plastic containers, high clamp forces are required to close the mold halves on the parisons to pinch off the plastic and to hold the mold halves closed during blow molding. Conventional mold clamp assemblies are mounted on the frame of the machine supporting the assembly and, when actuated, transmit clamping force from a drive on one side of the mold to the other side of the mold through the frame. This means that the frame supporting the molds must be sufficiently strong to counteract bending moments imposed by the high clamp force transmitted through the frame. Deformation of the frame by the clamp force is undesirable because deformation would not permit the mold faces to close parallel with one another.
In an attempt to improve upon existing technology, U.S. Pat. No. 7,611,657 discloses a mold clamp assembly for a rotary-type or shuttle-type blow molding machine. The clamp assembly is mounted on a frame and includes a mold opening and closing drive connected to the two mold halves independently of the frame, so that when the mold halves are closed, clamp forces are not transmitted to the mold halves through the frame. Consequently, the high clamp force required to hold the mold halves together during blow molding is not transmitted from one side of the mold to the other side of the mold through the machine frame.
The blow molding apparatuses described above are typically costly, heavy machines, which require a good deal of expertise to maintain. For example, when a mold clamp requires maintenance, the entire wheel must be taken off-line as the mold clamp is worked on. In addition, if the number of mold clamps of the blow molding apparatus are to be changed to accommodate molds of a different size, the cost and time required to disassemble and reassemble the apparatus is significant.
Accordingly, there is a need for an improved molding apparatus and mold clamp assembly which allows for ease of maintenance and ease of configuration of the apparatus. There is also a need to reduce the complexity of the molding apparatus to help reduce the cost of the manufacture and operation of the molding apparatus. In addition, there is a need to have a modular mold clamp assembly for accomplishing the above, in which the high clamp force required to hold the mold halves together during molding is not transmitted from one side of the mold to the other side of the mold through the machine frame.